Observations on the relationship between nerve supply and hair positioning in the rat vibrissa follicle.

The present study has demonstrated an anatomical relationship between the position of the growing and non-growing hairs of the rat vibrissa follicle and the point where the follicular nerve supply penetrates the follicle capsule circumference. This finding may be significant in relation to the sensory function of the follicle, as physiological data have shown that the degree of stimulation of brain cells following mechanical displacement of the whisker is direction dependent. The observed relationship between the nerve entry point and the hairs, therefore, may reflect an uneven distribution of nerve endings around the upper follicle circumference. In relation to hair growth, the above observation requires that the non-growing club hair must consistently move up one side of the follicle at the end of each growth cycle. A possible clue as to the mechanism by which club hair movement is directed can be derived from observation of asymmetry, both at the base of the club hair, and in the epidermal matrix near the end of the growth cycle.